1. Field of the Invention
The present invention relates to monolithic ceramic electronic components, and particularly to a monolithic ceramic capacitor manufactured by a method of reducing acoustic noise generated when an electric field is applied to the monolithic ceramic capacitor mounted on a circuit board.
2. Description of the Related Art
As electronic devices produce increasingly less noise, acoustic noise has become more noticeable, caused by vibrations of monolithic ceramic capacitors (referred to as “monolithic capacitors”, below) in power circuits or other components of various apparatuses, such as laptop computers, mobile phones, or digital cameras.
Japanese Unexamined Patent Application Publication No. 2010-186884 describes that acoustic noise occurs when an AC voltage is applied to a monolithic capacitor mounted on a circuit board due to electrostrictive vibrations of the monolithic capacitor propagating through the circuit board.
FIG. 5 and FIG. 6 are drawings illustrated on an online web page “Examples of Noise Countermeasures” of Murata Manufacturing Co., Ltd., searched on Mar. 1, 2012, through Internet URL “http://www.murata.co.jp/products/capacitor/solution/naki.ht ml”. When an AC voltage is applied to a monolithic capacitor 110, the monolithic capacitor 110 expands and contracts in directions indicated by the bold arrows, as illustrated in FIG. 5, due to the electrostrictive effect of the ferroelectric ceramic of the monolithic capacitor 110. In FIG. 5, the WT cross section denotes a cross section defined by the width and the thickness of the monolithic capacitor 110. The LT cross section denotes a cross section defined by the length and the thickness of the monolithic capacitor 110. The LW cross section denotes a cross section defined by the length and the width of the monolithic capacitor 110. The broken lines indicate the extent to which the monolithic capacitor 110 expands and contracts when viewed in these cross sections.
As illustrated in FIG. 6, when an AC voltage is applied to the monolithic capacitor 110 that is mounted on the circuit board 101 via a solder 102, the monolithic capacitor 110 expands and contracts and this expansion and contraction of the monolithic capacitor 110 leads to deformation of the circuit board 101 via the solder 102. Thus, the circuit board 101 vibrates in such directions that the surface of the circuit board 101 rises and falls. When the cycle of vibrations of the circuit board 101 falls within a frequency range (20 Hz to 20 kHz) that is audible to human beings, human ears perceive the vibrations as acoustic noise.
These are problems not only for the monolithic capacitor 110 having two outer electrodes 114 but also for a three-terminal monolithic capacitor having three outer electrodes 114. Further, these problems can occur not only in the monolithic capacitor 110, but also in any monolithic ceramic electronic component including a monolithic LC filter.